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This tutorial walks through three minimal workflows that introduce the building blocks of Fabro: a one-shot prompt, an agent with tool access, and a sub-agent delegation pattern.

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Prerequisites

Complete the Quick Start so you have a working fabro binary and at least one LLM API key configured.

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1. One-shot prompt

The simplest possible workflow has one node that sends a prompt to an LLM and exits.
Hello World workflow: Start → Compose → Exit
hello.fabro
digraph Hello {
    graph [goal="Write a haiku about software workflows"]
    rankdir=LR

    start [shape=Mdiamond, label="Start"]
    exit  [shape=Msquare, label="Exit"]

    compose [label="Compose", prompt="Write a haiku (5-7-5 syllable) about software workflows. Output only the haiku, nothing else.", shape=tab, reasoning_effort="low"]

    start -> compose -> exit
}
Run it: 
fabro run files-internal/demo/01-hello.fabro

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What’s happening

  • shape=tab makes this a prompt node — a single LLM call with no tool access. Good for generation, summarization, and classification.
  • reasoning_effort="low" tells the model to think less. This is a simple task that doesn’t need deep reasoning.
  • graph [goal="..."] describes the workflow’s purpose. Fabro uses it in preambles and retrospectives.
Every workflow needs exactly one start node (shape=Mdiamond) and one exit node (shape=Msquare).

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2. Agent with tools

An agent node (the default box shape) runs an LLM in a loop with access to tools — bash, file reading, file editing, grep, and glob. The agent calls tools autonomously until it decides the task is complete.
Tool Use workflow: Start → Explore → Exit
tool-use.fabro
digraph ToolUse {
    graph [goal="Explore the current directory using shell tools"]
    rankdir=LR

    start [shape=Mdiamond, label="Start"]
    exit  [shape=Msquare, label="Exit"]

    explore [label="Explore", prompt="Use bash to list the files in the current directory, then read the first 5 lines of any README or CLAUDE.md file you find. Summarize what this project is about in 2-3 sentences."]

    start -> explore -> exit
}

fabro run files-internal/demo/02-tool-use.fabro

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What’s happening

  • No shape attribute means the default box — an agent node.
  • The agent has access to built-in tools: shell, read_file, write_file, edit_file, grep, glob, web_search, and web_fetch.
  • The agent decides which tools to call and when to stop. Fabro handles the tool loop automatically.

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Prompt vs. agent nodes

Prompt node (tab)Agent node (box)
LLM callsSingle callMulti-turn loop
Tool accessNoneFull toolset
Use caseAnalysis, generationTasks requiring file I/O and commands

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3. Sub-agents

An agent can spawn sub-agents to delegate work. Sub-agents run in their own session and return results to the parent.
Sub-agent workflow: Start → Research → Exit
sub-agent.fabro
digraph SubAgent {
    graph [goal="Research and summarize using a sub-agent"]
    rankdir=LR

    start [shape=Mdiamond, label="Start"]
    exit  [shape=Msquare, label="Exit"]

    research [label="Research", prompt="You have a sub-agent available via the spawn_agent tool. Spawn a sub-agent to list the files in the current directory and read the first 10 lines of any README or CLAUDE.md. Then, using the sub-agent's findings, write a 2-sentence summary of the project."]

    start -> research -> exit
}

fabro run files-internal/demo/03-subagent.fabro

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What’s happening

  • The parent agent uses spawn_agent to create a child session, then wait to collect the result.
  • Sub-agents have their own tool access and conversation history — they don’t see the parent’s context.
  • This pattern is useful for parallelizing research, isolating risky operations, or keeping the parent’s context window lean.
See Sub-agents for the full tool reference.

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What you’ve learned

  • Prompt nodes (shape=tab) make a single LLM call — no tools
  • Agent nodes (default box) run a multi-turn tool loop
  • Sub-agents let an agent delegate to independent child sessions
  • Every workflow needs a start node, an exit node, and a goal

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Next

Plan & Implement

Add human gates and revision loops to a multi-step workflow.